If you have ever wished for ‘something’ to prevent delivery of any inappropriate mail you sent accidently. Well, here it is, Google mail’s new feature has that ‘something’ as ‘Undo send’. Google had been working on this feature of preventing the sending of accidently sent mails in its laboratory from last six years. It was first added last month in the whole new mailbox environment brought up by Google- Inbox’s mobile application. Undo send is now available in Google’s webmail.
Enabling undo send delays sending of mail by 10, 20 or 30 seconds (as per individual settings) which can be termed as cancellation period which a certain user gets to call their mail back. The feature- Undo send can be turned on from within Gmail settings menu.

“ Previously a popular feature in Gmail Labs, and recently added to Inbox by Gmail, today we’re adding 'Undo Send' as a formal setting in Gmail on the web.”, Google in a blog post.

“'Undo Send' allows people using Gmail to cancel a sent mail if they have second thoughts immediately after sending. The feature is turned off by default for those not currently using the Labs version, and can be enabled from the General tab in Gmail settings.”
Currently, there are ~900 million active Gmail users as per the statistics revealed by Google last month out of which 75% users access their mails using mobile devices. Google executive Sundar Pichai said that users would have to install company’s Inbox application to use undo send feature.
Here’s how to enable undo send.